This invention relates to the preparation of a tool wherein the work engaging surfaces of the tool have an abrasive or non-slip solid coating applied thereto. The invention is particularly suitable for use on tools which engage or grip a surface of an object, such tools including, for example, screwdrivers, wrenches, sockets, pliers, clamps and the like. Thus, the applicable range of tools include those used for turning fasteners such as screws, nuts and bolts, as well as providing a gripping or frictional holding force on an object.
In connection with screwdrivers, for example, well known types include the conventional blade screwdriver and the phillips. The bit end of the tool is inserted into a corresponding recess in the screw in a driving connection, and the handle of the screwdriver is turned in order to thread the screw into the work. As the threaded shank of the fastener increases its penetration or engagement with the material or work, the resistance may increase, and the torque required for the operation may also increase. This often causes the screwdriver head to slip or back out of the screw slot, usually causing dmage to the screw and sometimes to the screwdriver. This phenomenon is commonly referred to as "cam out." In order to reduce the severity and frequency of this occurrance, it is necessary to exert additional axial force on the screwdriver to hold it in driving engagement, but a point is eventually reached where slippage will occur. Similar problems with gripping and driving tools are commonplace and need not be described in detail.
There are several proposals in the prior art to provide screwdrivers with non-slip surfaces. The U.S. Pat. No. 3,133,568 to Reed discloses a screwdriver in which the tip has been shot blasted or peened, and scored. The Wickbergh U.S. Pat. No. 1,899,489 discloses a screwdriver having a knurled tip to prevent slippage.
Both of the above patents involve roughening of the metallic working surface of the tool. As the tool is used, however, additional pressure is placed on the raised areas of the roughened surface. As a result, the surface will wear down and lose its effectiveness, and the tool would become undersized or worn out.
Aother type of anti-slip screwdriver is described in U.S. Pat. No. 3,656,522. In this disclosure, an abrasive liquid is contained in the handle of the screwdriver and is fed through the shank to the tip in order to increase friction between the screwdriver tip and the screw recess. The construction of such a tool, however, would be expensive, handling would be difficult, and the tool would leave a residue of abrasive on the fastener.